AIM To investigate of pediatric ulcerative colitis activity index(PUCAI) in ulcerative colitis correlate with mucosal inflammation and endoscopic assessment of disease activity(Mayo endoscopic score).METHODS We reviewed charts from ulcerative colitis patients who had undergone both colonoscopy over 3 years. Clinical assessment of disease severity within 35 d(either before or after) the colonoscopy were included. Patients were excluded if they had significant therapeutic interventions(such as the start of corticosteroids or immunosuppressive agents) between the colonoscopy and the clinical assessment. Mayoendoscopic score of the rectum and sigmoid were done by two gastroenterologists. Inter-observer variability in Mayo score was assessed.RESULTS We identified 99 patients(53% female, 74% pancolitis) that met inclusion criteria. The indications for colonoscopy included ongoing disease activity(62%), consideration of medication change(10%), assessment of medication efficacy(14%), and cancer screening(14%). Based on PUCAI scores, 33% of patients were in remission, 39% had mild disease, 23% had moderate disease, and 4% had severe disease. There was “moderate-substantial” agreement between the two reviewers in assessing rectal Mayo scores(kappa = 0.54, 95%CI: 0.41-0.68). CONCLUSION Endoscopic disease severity(Mayo score) assessed by reviewing photographs of pediatric colonoscopy has moderate inter-rater reliability, and agreement was less robust in assessing patients with mild disease activity. Endoscopic disease severity generally correlates with clinical disease severity as measured by PUCAI score. However, children with inflamed colons can have significant variation in their reported clinical symptoms. Thus, assessment of both clinical symptoms and endoscopic disease severity may be required in future clinical studies. AIM To investigate of pediatric ulcerative colitis activity index (PUCAI) in ulcerative colitis correlate with mucosal inflammation and endoscopic assessment of disease activity (Mayo endoscopic score). METHODS We reviewed charts from ulcerative colitis patients who had undergone both colonoscopy over 3 years. of patients severity within 35 d (either before or after) the colonoscopy were included. The patients were excluded if they had significant therapeutic interventions (such as the start of corticosteroids or immunosuppressive agents) between the colonoscopy and the clinical assessment. Mayoendoscopic score of the rectum and sigmoid were done by two gastroenterologists. Inter-observer variability in Mayo score was assessed .RESULTS We identified 99 patients (53% female, 74% pancolitis) that met inclusion criteria. The indications for colonoscopy included ongoing disease activity (62%), consideration of change (10%), assessment of medication efficacy (14%), and cance Based on the PUCAI scores, 33% of patients were remission, 39% had mild disease, 23% had moderate disease, and 4% had severe disease. There was “moderate-substantial ” agreement between the two reviewers assessing rectal Mayo scores (kappa = 0.54, 95% CI: 0.41-0.68). CONCLUSION Endoscopic disease severity (Mayo score) assessed by photographs of pediatric colonoscopy has moderate inter-rater reliability, and agreement was less robust in assessing patients with mild disease activity. However, children with inflamed colons can have significant variations in their reported clinical symptoms. Thus, assessment of both clinical symptoms and endoscopic disease severity be required in future clinical studies.